Piano keying circuit for electrical musical instrument,with selective by-pass circuits for other instrumental effects



June 2 1970 F minnow 3,515,191

PIANO KEYING CIRCUIT FOR ELECTRICAL MUSICAL INSTRUMENT, WITH SELECTIVEvBI -PASS CIRCUITS FOR OTHER INSTRUMENTAL EFFECTS Filed June 22, 1966TONE GE NEIZATOR INVENTOR.

Hoyb A. CORDR ATTORNEY United States Patent 01 3,515,791 Patented June2, 1970 PIANO KEYING CIRCUIT FOR ELECTRICAL MUSICAL INSTRUMENT, WITHSELECTIVE BY-PASS CIRCUITS FOR OTHER INSTRU- MENTAL EFFECTS Floyd A.Cordry, Granada Hills, Calif., assignor to Warwick Electronics Inc.,Chicago, 11]., a corporation of Delaware Filed June 22, 1966, Ser. No.559,548 Int. Cl. Gh 1/00, 1/02 US. Cl. 841.01 8 Claims ABSTRACT OF THEDISCLOSURE A keying circuit is provided for an electrical musicalinstrument which permits the artist to simulate piano tones, and whichincludes a plurality of bypass circuits which may be selectivelyactuated for other tonal efiects.

This invention relates to keying circuit for an electrical musicalinstrument. By means of this keying circuit, the artist or performermay, at will, select various tonal envelopes for the tones produced,such as piano or harpsichord, organ, organ with percussion attack, andaccordion.

It is known to provide a keying circuit for an electronic musicalinstrument by means of which piano tone envelopes may be simulated. Suchcircuits have consisted, for example, of a plurality of key switches,one for each key of a keyboard instrument; a corresponding plurality ofkeyers, which, when appropriately stimulated, serve to apply anappropriate tone or tonal combination to the loudspeaker of the system;and a piano circuit connecting the key switch to the keyer. The pianocircuit includes a series connected capacitor through which a pulse ofcurrent passes, as the capacitor is charged, to stimulate or activatethe keyer with a pulse which simulates the envelope of a piano tone whena piano key is struck.

In accordance with the present invention, by-pass circuit means areprovided, whereby other instrumental elfects, such as organ oraccordion, may be developed at the will of the performer, by theoperation of suitable stops or tabs which operate switches linkedthereto.

Circuit means are provided in accordance with this invention to allowthe operator to select a sostenuto or sustain elfect.

Also in accordance with this invention, means are provided to achievethe unique, short, initial percussive efiect characteristic of thestriking of a piano hammer against the piano strings.

A preferred form of the present invention will now be described inconjunction with the single drawing, which is a circuit diagram of akeyer circuit in accordance with the present invention.

In the drawing, 11 represents one of a plurality of keyboard keys on thekeyboard of a musical instrument. Associated with each key 11 is a keyswitch means illustrate-d specifically here as a single-pole,single-throw switch 12, which is normally open and which is closedwhenever the performer depresses the key 11. "13 is a keyer meanscorresponding to the key 11, which, when appropriately stimulated, inaccordance with the present invention, applies to its output 14 a signalor voltage of appropriate configuration that, in due course, becomeseffectively the envelope for the audio tone sounded by the instrument.In the present circuit, it is contemplated that the output applied at 14will in turn be used to open or render conductive or operative anappropriate modulator, keyer, oscillator, or other form of audio gate,to apply audio tone signals to the acoustic output of the instrument.The output gating circuit is shown generally at 15, the ground implyingthat it thus serves as a return path for currents passing through thekeyer means 13. If desired, the keying means 13 may itself constitutethe audio gate, which case audio tones would be applied directly to thekeying means 13 and upon appropriate stimulation, audio would pass intoand out of the keying means.

Piano circuit means 16 serves to connect the switch 12 to the keyer 13,so as to pulse-activate the keyer 13 every time the switch 12 is closed.The circuit 16 includes a capacitor 17, connected in series betweenswitch 12 and the keyer 13, a resistor 18, and diode 19. The diagonalline 21 represents a bus which is common to a plurality of keys 11, suchas a given keyboard, or in fact, if desired, all of thejkeys of theinstrument. The bus 21 is connected to a positive source of voltage,shown by way of example as a plus 14 volt source 22. Upon closing of theswitch 12, a pulse of current passes from the source 22, through thecapacitor 17, and to the keyer 13. In so doing, it quickly andmomentarily charges a capacitor 23 which functions to provide sustain orsostenuto.

When the switch 12 is opened, it is desirable for fast repeating thatthe capacitor 17 be quickly returned to quiescent (nominally discharged)condition. To this end, a diode 24 is provided, which serves in adischarge circuit for the capacitor 17, in a manner which will beexplained hereinafter.

As will be explained more fully hereinafter, the circuit heretoforedescribed provides for pulse activation of the keyer 13 whenever theswitch 12 is closed. In accordance with the present invention, there isalso provided circuit means for achieving, at the will of the performer,either an organ simulating condition, or an accordion simulatingcondition; so that when appropriate tabs are operated, the depression ofthe key 11 will produce, not a piano simulating envelope, but an organor an accordion simultating envelope. To this end, for organ simulation,a by-pass circuit means 26 is provided which by-passes the piano circuitmeans 16 to apply a non-percussion stimulus to the keyer 13, so long asthe key switch 12 remains closed. Specifically, this by-pass consists ofa series connected resistor 27 and diode 28 connected between the key 12and the circuit point 29 to the right of the diode 19.

In accordance with the present invention, means are provided fordisabling the by-pass circuit 26 so as to render it ineffective to applya non-percussive stimulus to the keyer 13. This means employs the diode28 as one of a pair of back-to-back diodes, the other one of which isshown at 31. This is achieved by connecting the diode 31 to the juncturebetween the resistor 27 and the diode 28. The other side of the diode 31is connected through a singlepole, single-throw switch 32 to a terminal33 having a potential of minus five volts. Terminal 33 in effect thusreturns to the other side of the source 22, but is at minus five voltsrelative to a zero reference (ground) with respect to which the terminal22 is biased by plus fourteen volts. The by-pass circuit 26 serves toapply an organ simulating keying stimulus or signal to the keyer 13.

In order to simulate an accordion, a bypass circuit 36, similar to thecircuit 26, parallels the circuit 26. It consists of a resistor 37,diodes 38 and 39, and switch 41, returning to the minus five voltterminal 33. An interlock, represented schematically at 40, is providedbetween switches 32 and 41 to prevent both of the switches from beingopen at the same time. The purpose of this interlock will becomeapparent hereinafter. In order to disable or render ineifective thepiano keying circuit 16, when either of the circuits 26 or 36 is to beemployed, there is provided a disabling means consisting of a diode 42,through which the terminal point 43 to the left of the diode 19 isgrounded at 44 by way of a single-pole switch 46.

The keyer 13 consists of a transistor, the base 47 of which constitutesthe input that receives the stimulating voltage initiated through theswitch 12. The collector 48 is connected to a bus 49, which in turn isconnected through a double-throw switch 51, either to a terminal 52 onwhich resides plus 11.2 volts or a terminal 53 on which resides plus 5.8volts. The transistor 13 is connected as an emitter follower, so thatthe emitter 54 constitutes the output terminal 14 discussedhereinbefore.

The circuitry interposed between the switch 12 and the keyer 13 includesa series connected resistor 56. In accordance with the presentinvention, a capacitor 57 is connected in shunt with the resistor 56 toprovide a small initial surge of voltage to the keyer 13, which effectssimulation of the striking of a piano hammer against the piano strings.This effect may be negated by connecting the collector 48 to the plus5.8 voltage source 53, as will be explained hereinafter.

In accordance with the present invention, sustain circuit means 61 areprovided. This circuit in the case of piano operation is associated withthe simulation of sostenuto, and in the case of organ operation, withorgan sustain. The circuit includes a resistor 62 connected through adiode 63 to the junction point 29. The other end of the resistor 62 isconnected to a bus 64 and thence through a switch 66 to a double-throwswitch 67, the terminals of which are connected respectively to ground68 and to 3.5 volts shown at 69. The bus 64 is returned to the plusfourteen volt terminal 22 through a resistor 71. Diode 70, by applying areverse bias to diode 63 while switch 12 is closed, prevents currentfrom being b-led away from point 29 through sostenuto path 61.

The sustain or decay characteristics of the tone are also controlled bya discharge circuit consisting of resistor 72 connected to the base 47and leading to a potentiometer 73, connected between ground 74 and minusfive volts at 76. A switch 77 is provided to isolate the potentiometer73 from the minus five volt potential, if desired.

It is to be understood that the various potentials referred to representvoltage levels all referred to a common reference of which the groundsymbol represents zero voltage. It will be further understood that ineach case the diagonal lines exemplified by the bus 21 represent busescommon to a plurality of keys 11. The components below each of theseveral buses are likewise common to a plurality of keys. Thus, forexample, the switches 32, 41, and 46 are common to a plurality ofcircuits, one of which is described in the figure. By the term diodeused herein is meant broadly any unilateral conducting device which has,in the operating ranges of this circuit, a very high resistance in onepolarity and a very low resistance in the opposite polarity.

Function and operation of the circuit illustrated will now be described.

PIANO OR HARPSICHORD If a piano or harpsichord effect is desired, theswitches are set, through appropriate tab operation, as follows: switch32 closed; switch 41 closed; switch 46 open; switch 77 closed; switches51 and 67 in upper position.

The sostenuto switch 66 is normally biased to closed position. It isopened, usually by a knee control, by the performer whenever he wishesto simulate depression of the sostenuto pedal of a piano (or organsustain).

In quiescence, with switch 12 open, capacitor 17 will have a minus fivevolt charge thereon, from the minus five volt potential 33. Source ofthis charge may be traced from ground 81 through diode 24 (and resistor82), capacitor 17, resistor 27, diode 31, switch 32 to the minus fivevolt terminal 33. Upon closing of a key switch 12, plus 14 volts isapplied to the capacitor 17 from the source 22. There is thus in effecta l9-volt potential difference, causing current to flow through thecapacitor 17,

resistor 18, diode 19, capacitor 57 (and resistor 56), the

base 47 of the transistor keyer 13, and thence through the outputcircuit 15. This forward biases the emitter follower to cause current toflow from the collector 48 to 4 the emitter 54 and thence through theoutput lead 14 to the gating circuits 15, which complete the keyingfunction and allows tone signal to flow from the tone generators to theacoustic output system, such as the loudspeaker 92.

Capacitor 23 is much smaller than capacitor 17. Thus, when capacitor 17starts to charge, capacitor 23 becomes substantially fully charged veryquickly, because of the relatively small effective impedance in seriestherewith, represented by 17, 18, and 19. Thereafter 17 charges moreslowly, primarily through resistor 82, while capacitor 23 dischargesthrough resistance 56 and the base/emitter junction of 13, and alsothrough resistor 72 to the potential determined by the slider on thepotentiometer 73. As long as the switch 12 remains closed, thisphenomenon continues until 17 becomes fully charged and 23 becomes fullydischarged. The result is a pulse, Le. a rise, and then a fall, ofvoltage on base 47, producing a pulse at the output 14, the nature ofwhich simulates the configuration of the envelope of a piano tone.

When switch 12 is opened, the discharge of capacitor 23 is alsoconsiderably influenced by the discharge path through diode 63, resistor62, to bus 64, sostenuto switch 66 and thence to the biasing terminal 68or 69.

A staccato effect is achieved if the key switch 12 is opened before 17is fully charged. When this happens the capacitor 17 immediately beginsto discharge. This reverses the polarity of the voltage across resistor82, forward biases diode 24, and reverse biases diode 19. Discharge ofcapacitor 23 is accelerated through the sostenuto resistor 62. Thisresults in termination of the tone which, while abrupt, is notcompletely instantaneous, since there is some small tail effectedthrough the remnant of charge on the capacitor 23.

If this opening of the switch 12 is effected with the sostenuto switch66 open, then there is a long decay period in the pulse, because thedischarge path for the capacitor 23 is limited to the keyer 13 and theresistor 72. The tone is thus prolonged to simulate the effect of apiano with the sostenuto pedal depressed.

As noted above, the playing of a key and closing of a switch 12 placescapacitor 17 in a positive charged condition, i.e. The left side of 17is positive with respect to the right side. When the switch 12 isopened, it is desirable to quickly discharge (and than reverse charge)capacitor 17, in order to ready the circuit for the possible replayingof the key, as when notes are played in rapid succession on a piano.This is effected in the present circuit by the diode 24 which provides adischarge path for the capacitor 17 through elements 27, 31, 32, 33, 81,24, and back to the capacitor 17.

The function of the capacitor 57 is to provide an overshoot in theinitial voltage rise at the base 47 whenever the key 12 is closed. Thismodifies the pulse so that, when formed into a tone envelope, itsimulates the striking of the hammer on a piano string.

The chief reason for the interlocking of switches 32 and 41, to assurethat at least one of these switches will always be closed, is to assuremaintenance of this discharge path for capacitor 17 through the diode24. Furthermore, when properly played, there should be no occasion forthe performer to have 32 and 41 open simultaneously, since this wouldrepresent a setting of the stop tabs simultaneously for organ andaccordion, which, of course, is a musical incompatibility.

ORGAN CIRCUIT the diode 42. Closing the switch 41 effectively reversebiases diode 38 by applying minus five volts to the righthand side ofresistor 37. This leaves the circuit consisting of resistor 27 and diode28 as the only on which can transmit current to the keyer from theswitch 12.

Upon closing of switch 12, current flows through 27 and 28 to chargecapacitor 23, thus causing the desired tone to sound. The piano hammereffect present in the operation of the piano circuit, because of theovershoot through capacitor 57, is eliminated by placing the collector49 at 5.8 volts, instead of 11.2. This is because the drive provided bythe overshoot through capacitor 57 takes the transistor base beyond theeffective gain range of the transistor, when the collector has only a5.8 volt bias. As a result, the overshoot passes directly from base 47to emitter 54 without gain, and is for practical purposes lost.

Since there is now a direct current path from the source 22 to the keyer13, the tone is sustained as long as the switch 12 remains closed. Whenthe switch 12 is opened, the charge on capacitor 23 quickly, althoughnot instantaneously, dissipates through the sostenuto resistor 62. Ifthe knee-operated switch 66 is open, the only discharge path for 23 isthrough resistor 56 and thence through the dual path represented bykeyer 13 and resistor 72. Thus along sustain tone is produced, thelength of which is dependent upon the setting of the slider ofpotentiometer 73.

For conventional organ simulation, it is preferred to have a very, veryshort sustain time. To this end, the sostenuto circuit is groundedthrough switch 67 and the resistor 72 is returned to a negative voltageby the closing of switch 77.

ORGAN WITH PERCUSSIVE ATTACK To simulate an organ with percussiveattack, the switch positions are the same as described above for theorgan, except that switch 46 is open, thereby placing the piano keyingcircuit 16 also into operation. In addition, the switch 51 is placed inits upper position, thereby bringing the effect of capacitor 57 backinto the picture. Finally, it is preferred for this mode of operation toopen switch 77, thereby giving a somewhat longer sustain time which maybe musically desirable with very sharp attack.

The operation in this mode represents simply a combination of theoperation of the piano and the organ circuits described hereinbefore.This in effect means that the attack is a sharp, abrupt attack as withthe piano, but the tone continues as in an organ, as long as switch 12remains closed.

ACCORDION To simulate an accordion tone, the switches are placed asfollows: 32 closed; 41 open; 46 closed; 77 open; 51 and 67 in upperposition.

Accordion operation is essentially similar to organ operation, exceptthat the attitude of switches 32 and 41 is interchanged. This bringsinto play the by-pass resistor 37 instead of the resistor 27. Resistor37 is considerably larger than is resistor 27, thus producing a muchlonger attack time, since the charging time for capacitor 23 is thusmuch longer. Additionally, it is preferred to have a short sustain andto this end the switch 67 is placed in the upper position in which thesostenuto circuit is returned to 3.5 volts. In similar vein, by openingswitch 77, a somewhat longer sustain is also brought about.

While it is preferred to place switch 51 in the upper position, therebybiasing the collector to 11.2 volts, the effect of the position ofswitch S1 in accordion operation is virtually negligible. This isbecause, irrespective of what the collector voltage is, the charging ofcapacitor 23 is so slow that the overshoot capacitor 57 can have littleeffect, irrespective of the collector bias.

The operation of the sostenuto circuit 61 is as follows:

The closing of a key switch 12 forward biases diode 70 and reversebiases diode 63. When the switch 12 is opened, however, the condition isreversed; diode 63 is forward biased while diode 70 is reverse biased.This permits rather rapid discharge of capacitor 23 through resistor 62,down to whatever voltage level is set by the switch 67. When thesostenuto switch 66 is operated to open position, the principaldischarge path for capacitor 23 is removed, thus causing the note to besustained, in all modes of operation: organ, piano, and accordion.

As an example, a circuit having the following parameters has beenoperated very successfully.

' Capacitor 17 .40 microfarads.

Resistor 72 has four values as shown, because the notes of the scalewere divided into four groups, having the four values shown above.

Whereas the present invention has been shown and described herein inwhat is conceived to be the best mode contemplated, it is recognizedthat departures may be made therefrom within the scope of the inventionwhich is, therefore, not to be limited to the details disclosed herein,but is to be afforded the full scope of the invention as hereinafterclaimed.

What is claimed is:

1. In a keying circuit for an electrical musical instrument having:

key switch means, keyer means, and piano circuit means, including acapacitor connected in series between said key switch means and saidkeyer means, for causing said keyer means to be pulse-actuated by saidpiano circuit means upon operation of said key switch means, thereby tosimulate the envelope of a piano or harpsichord; the combinationcomprising:

by-pass circuit means by-passing said piano circuit means for applying acontinuous stimulus to said keyer means so long as said key switch meansremains in operated position thereby to simulate a non-percussioninstrument, such as an organ,

by-pass circuit disabling means for selectively rendering said by-passcircuit means ineffective to apply said continuous stimulus to saidkeyer means, and

piano circuit disabling means for selectively rendering said pianocircuit means ineffective to pulseactuate said keyer means.

2. The combination of claim 1 wherein said piano circuit meanscomprises:

piano circuit diode means connected in series between said capacitor andsaid keyer means, said combination including,

a source of direct voltage having one side connected to have its voltageapplied to said capacitor upon operation of said key switch means, andwherein said by-pass circuit means shunts said series-connectedcapacitor and diode means.

3. The combination of claim 2 in which said piano circuit disablingmeans comprises:

series-connected diode means and switch means connected to said pianocircuit means between said capacitor and said piano circuit diode means,

circuit means for returning said series-connected diode means and switchmeans to the other side of said voltage source and wherein,

said by-pass circuit disabling means comprises a pair of back-to-backdiodes, one being connected in that portion of said by-pass circuitmeans which shunts said series-connected capacitor and diode means, the

other being connected to a circuit returning to the other side of saidvoltage source. 4. The combination of claim 2, including a sustaincapacitor connected to said keyer means, and

sostenuto circuit means connected between said sustain capacitor and theother side of said source. 5. In a keying circuit for an electricmusical instrument having:

key switch means, keyer means, piano circuit means comprising:

capacitor means and diode means connected in series between said keyswitch means and said keyer means,

a source of direct voltage having one side connected to have its voltageapplied to said capacitor means upon operation of said key switch means,

a sustain capacitor connected to said keyer means for providing asostenuto elfect, the combination comprising,

selectively actuable sostenuto-defeating circuit means connected betweensaid sustain capacitor and said key switch means for rapidly dischargingsaid sustain capacitor upon release of said key switch means.

6. In a keying circuit for an electric musical instrument 1 having:

key switch means, keyer means, piano circuit means comprising:

capacitor means and diode means connected in series between said keyswitch means and said keyer means,

a source of direct voltage having one side connected to have its voltageapplied to said capacitor means upon operation of said key switch means,

a sustain capacitor connected to said keyer means for providing asostenuto effect, the combination comprising,

sostenuto-defeating circuit means connected to said sustain capacitor todischarge the same, said sustenuto-defeating circuit means comprising:

a first diode having one side connected to said keyer means, circuitmeans for returning the other side of said first diode to the other sideof said voltage source, and a second diode connected between said keyswitch means and the other side of said first diode. 7. In a keyingcircuit for an electrical musical instrument having:

8 key switch means, keyer means, and piano circuit means, including acapacitor connectedin series be tween said key switch means and saidkeyer means, for causing said keyer means to be pulse-actuated by saidpiano circuit means upon operation of said key switch means, thereby tosimulate the envelope of a piano or harpsichord; the combinationcomprising:

by-pass circuit means by-passing said piano circuit means for applying acontinuous stimulus to said keyer means so long as said key switch meansremains in operated position thereby to simulate a non-percussioninstrument, such as an organ, and

by-pass circuit disabling means for selectively rendering said by-passcircuit means inefiective to apply said continuous stimulus to saidkeyer means, said by-pass circuit disabling means comprising gatingmeans and means for selectively biasing said gating means to conductionor nonconduction condition.

8. A keying circuit for an electric musical instrument having a keyswitch, keyer means, and a source of direct voltage connected to applykeying potential to said keyer means upon operation of said key switch,characterized by said keyer means including:

a transistor having at least an input terminal and a biasing terminal,

parallel capacitor and resistor circuit means connected between said keyswitch and said input terminal for providing a voltage overshoot uponactuation of said key switch, and

biasing means connected to said biasing terminal of said transistor forapplying a plurality of significantly dilferent biasing voltages to saidbiasing terminal,

one of said biasing voltages having a value 'which renders said voltageovershoot from said parallel capacitor and resister circuit meansineffective.

References Cited UNITED STATES PATENTS 3,408,449 10/ 1968 Tinker 84-126X 2,906,959 9/1959 Peterson 841.25 X 3,196,201 7/1965 McDonald 84-1263,247,306 4/1966 Milho 841.13 3,309,454 3/1967 Gitzer et a1. 84-1.033,383,453 5/1968 Sharp 84-1.2.6 3,389,211 6/1968 Slaats 841.13 X

HERMAN K. SAALBACH, Primary Examiner S. CHATMON, JR., Assistant ExaminerUS. Cl. X.R. 841.24, 1.26

